Spray inside of 3-1/2-quart slow cooker with cooking spray. Place onion over the bottom of slow cooker. Add the following ingredients in this order: carrots, celery, potatoes and beef. Sprinkle with thyme. Pour undrained tomatoes and water over the top of the beef. Cover; cook on LOW 8 to 10 hours or until meat is tender. Stir in tomato paste. Cover; cook 10 minutes more on HIGH.